Development and applications of Optogenetic tools for manipulation of cyclic nucleotides

Optogenetic manipulation of cells or organisms became successful in neuroscience, especially with the introduction of the light-gated ion channel Channelrhodopsin-2 as an easily applicable tool. The optogenetic toolbox was enriched with the application of earlier discovered and engineered photoreceptors, or newly discovered photoreceptors from nature. The application field was expanded from neuroscience to other fields like cardiovascular research etc. Recently, an optogenetic approach was also clinically applied for partial recovery of visual function in a blind patient. Cyclic nucleotides, specifically cAMP and cGMP, play pivotal roles as ubiquitous second messengers, governing a myriad of biological processes. The dysregulation of cyclic nucleotide signaling is implicated in various diseases, rendering it a crucial focus in pharmaceutical research. The application of optogenetics to manipulate cAMP was initially demonstrated by expressing the photoactivated adenylyl cyclase from the unicellular alga Euglena gracilis (EuPAC) in Drosophila melanogaster. Subsequently, the discovery of a much smaller PAC from the soil bacterium Beggiatoa (bPAC) has greatly advanced the field, providing an efficient tool for intracellular cAMP manipulation in genetically targeted cells. The bPAC was mutated into a photoactivated guanylyl cyclase (GC) for optogenetic manipulation of cGMP but showed low efficacy. Later, a natural light-gated guanylyl cyclase, Cyclop, was characterized from the fungus Blastocladiella emersonii, and determined to be the first enzyme rhodopsin with 8 transmembrane helices. In addition, new enzyme rhodopsin with light-gated PDE activity was discovered from a protist Salpingoeca rosetta. I present recent progress with light-gated GCs and PDEs for optogenetic manipulating cGMP.